Technical Guide P92x/EN CM/E11
Commissioning Guide
MiCOM P921-P922-P923 Page 9/28
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4.1.2 Insulation
Insulation resistance tests are only necessary during commissioning if it is required for
them to be done and they haven’t been performed during installation.
Isolate all wiring from the earth and test the insulation with an electronic insulation
tester at a DC voltage not exceeding 500V. Terminals of the same circuits should be
temporarily connected together.
The main groups of relay terminals are:
a) Voltage transformer circuits.
b) Auxiliary voltage supply.
c) External voltage output and opto-isolated inputs.
d) Relay contacts.
e) RS485 communication port.
f) Case earth.
The insulation resistance should be greater than 100MW at 500V.
4.1.3 On completion of the insulation resistance tests, ensure all external wiring is correctly
reconnected to the relay.
4.1.4 External wiring
Check that the external wiring is correct to the relevant connection diagram or
scheme diagram.
If an MMLG test block is provided, the connections should be checked against the
scheme (wiring) diagram. It is recommended that the supply connections are to the
live side of the test block (coloured orange with the odd numbered terminals (1, 3, 5,
7 etc.)). The auxiliary supply is normally routed via terminals 13 (supply positive) and
15 (supply negative), with terminals 14 and 16 connected to the relay’s positive and
negative auxiliary supply terminals respectively. However, check the wiring against the
schematic diagram for the installation to ensure compliance with the customer’s
normal practice.
4.1.5 Watchdog contacts
Using a continuity tester, check that the normally closed watchdog contacts are in the
states given in Table 1 for a de-energised relay.
Terminals Watchdog contacts
Relay de-energised Relay energised
35-36 Closed Open
36-37 Open Closed
TABLE 1 : WATCHDOG CONTACT STATUS
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